We. Jokela et Gw. Randall, FATE OF FERTILIZER NITROGEN AS AFFECTED BY TIME AND RATE OF APPLICATION ON CORN, Soil Science Society of America journal, 61(6), 1997, pp. 1695-1703
Management of fertilizer N on corn (Zea mays L.) fan greatly affect th
e efficiency of N use and the potential for adverse environmental effe
cts. Field studies were conducted on two nonirrigated southern Minneso
ta soils -a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquo
ll) and a Mt. Carroll silt loam (fine-silty, mixed, mesic Mollic Haplu
dalf) -to determine the effect of time and rate of N application on re
covery of fertilizer-derived N (FDN) in corn grain and stover and in t
he soil. Nitrogen rates of 75 and 150 kg ha(-1) on the Mt. Carroll soi
l and 100 and 200 kg ha(-1) on the Webster were applied at planting or
at the eight-leaf stage as (NH4)(2)SO4 to the same plots from 1982 to
1984. Enriched N-15 was applied to separate microplots each of the fi
rst 2 Sr to allow measurement of FDN. Grain yield responded to applied
N in 5 of 6 site-yr, but not to time of application. Uptake of FDN in
grain was increased by higher N rate in all cases, but by delayed app
lication in only one site-gear. Total plant FDN recovery ranged from 3
1 to 60% at the low N rate and from 24 to 45% at the high rate. Both y
ields and FDN recovery were affected by unusually drg midseason condit
ions. Fertilizer-derived N recovery from the soil after harvest ranged
from 25 to 56%, with a large proportion at the high N rate in inorgan
ic forms, especially with the late application, which increased the po
tential for leaching losses. Residual uptake of FDN by grain ranged fr
om 1 to 10% of the initial N rate. The difference method for estimatin
g FDN recovery gave different results from the N-15 method, emphasizin
g the importance of examining both labeled and nonlabeled N pools for
complete interpretation of N-15 studies.